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Chapter 1 Understanding Mail Service 13
The following image gives an overview of how the components of Mac OS X Server
Mail service interact:
Mac OS X Server
External Mail
Transfer Agent (MTA)
Native Mail
User Agent (MUA)
Web Browser
Optional
Mail Delivery Agent
Mail Delivery Agent
(Squirrel Mail)
Mail Transfer Agent (MTA)
SMTP Server (Postfix)
Dovecot
POP Server
IMAP Server
Virus Scanner
(ClamAV)
Spam Filter
(Spam Assassin)
Message storage
on disk in
Maildir format
Mail Transfer Agent
Simple Mail Transfer Protocol (SMTP) is a protocol used to send and transfer mail. SMTP
queues outgoing mail messages from the user. These messages are transferred over
the Internet to their destinations, to be picked up by incoming mail protocols.
Mac OS X Server uses Postx as its mail transfer agent (MTA). Postx fully supports
SMTP. Your mail users will set their mail application’s outgoing mail server to your
Mac OS X Server running Postx.
Postx is easy to administer. Its basic conguration can be managed through Server
Admin and therefore it does not rely on editing the conguration le.
Postx uses multiple layers of defense to protect the server computer from intruders:
There is no direct path from the network to the security-sensitive local delivery tools. Â
Postx does not trust the contents of its queue les or the contents of its IPC messages. Â
Postx lters sender-provided information before exporting it via environment Â
variables.